ENH: adjust wrapping routines for new vtkCellArray definition
- the vtkCellArray internal structure was still largely oriented on the VTK legacy format, but has now been revised. https://gitlab.kitware.com/vtk/vtk/merge_requests/5682 The `VTK_CELL_ARRAY_V2` define from vtkCellArray.h indicates that the newer version is being used. * In VTK-8.2.0 and older, sizes are interwoven (prefixed) in the connectivity. Connectivity: [n1, verts..., n2, verts... ] When using these in vtkUnstructuredGrid, also needed a secondary list of offsets for each of the starting locations. * The update version now resembles a CompactListList. For example Connectivity: [verts..., verts... ] Offsets: [0, n1, n1+n2, n1+n2+n3... ] The offsets are properly handled within vtkCellArray, and dropped as an additional input for vtkUnstructuredGrid.